Tridens

Plants perennial; usually cespitose, often with short, knotty rhizomes, occasionally with elongate rhizomes, never stoloniferous. Culms 5-180 cm, erect, mostly glabrous, lower nodes sometimes with hairs. Sheaths shorter than the internodes, open; ligules membranous and ciliate or of hairs; blades 6-25 cm long, 1-8 mm wide, flat or involute, margins not thick and cartilaginous. Inflorescences terminal, usually panicles (sometimes reduced to racemes), 5-40 cm, exceeding the upper leaves, exserted. Spikelets 4-10(13) mm, laterally compressed, with 4-11(16) florets, more than 1 floret bisexual; sterile florets distal to the fertile spikelets; disarticulation above the glumes. Glumes from shorter than to equaling the distal florets; lower glumes 1(3)-veined; upper glumes shorter than or about equal to the lower glumes, 1-3(9)-veined, unawned; calluses usually glabrous, sometimes pilose; lemmas hyaline or membranous, 3-veined, veins usually shortly hairy below, apices rounded to truncate, emarginate to bilobed, midvein often excurrent to 0.5 mm, lateral veins not or more shortly excurrent; paleas glabrous or shortly pubescent on the lower back and margins, veins glabrous or ciliolate; lodicules 2, free or adnate to the palea; anthers 3, reddish-purple. Caryopses dorsiventrally compressed and reniform in cross section, dark brown; embryos about 2/5 as long as the caryopses. x = 10.

Distribution

Conn., N.J., N.Y., D.C, Del., Ill., Ind., Kans., Mich., Minn., Nebr., N.Mex., Nev., Ohio, Okla., Wis., W.Va., Ont., Fla., N.H., Ariz., Tex., La., N.C., Tenn., S.C., Pa., Ala., Calif., Va., Colo., Md., Mass., R.I., Vt., Ark., Ga., Iowa, Utah, Mo., Miss., Ky.

Discussion

Tridens, a genus of 14 species, is native to the Americas; all ten species described here are native to the the Flora region. Hitchcock (1951) included both Erioneuron and Dasyochloa in Tridens; Tateoka (1961) demonstrated that they should be excluded. One of the differences between Tridens and the other two genera lies in their chromosome bases numbers, 10 in Tridens and 8 in Erioneuron and Dasyochloa. Tridens albescens is exceptional within Tridens in having chromosome numbers that suggest two base numbers, 10 and 8.

Selected References

Burbidge, N.T. 1953. The genus Triodia R. Br. (Gramineae). Austral. J. Bot. 1:121-184

Gould, F.W. 1975. The grasses of Texas. Texas A&M University Press, College Station, Texas, U.S.A. 653 pp.

Hitchcock, A.S. 1951 [title page 1950]. Manual of the Grasses of the United States, ed. 2, rev. A. Chase. U.S.D.A. Miscellaneous Publication No. 200. U.S. Government Printing Office, Washington, D.C., U.S.A. 1051 pp.

Tateoka, T. 1961. A biosystematic study of Tridens (Gramineae). Amer. J. Bot. 48:565-573.

Lower Taxa

Tridens albescens, Tridens ambiguus, Tridens buckleyanus, Tridens carolinianus, Tridens congestus, Tridens eragrostoides, Tridens flavus, Tridens muticus, Tridens strictus, Tridens texanus

Key

1	Primary panicle branches appressed to strongly ascending; panicles 0.3-4 cm wide, dense and spikelike.	> 2
2	Lateral veins of the lemmas glabrous or pubescent only at the base	Tridens albescens
2	Lateral veins of the lemmas pilose to well above the base.	> 3
3	Glumes evidently longer than the adjacent lemmas, often twice as long, usually equaling or exceeding the distal florets	Tridens strictus
3	Glumes from shorter than to equaling the adjacent lemmas, often exceeded by the distal florets.	> 4
4	All 3 lemma veins shortly excurrent; calluses pilose	Tridens carolinianus
4	Lateral lemma veins not excurrent, often terminating before the distal margin, the midvein sometimes excurrent; calluses glabrous or shortly pilose.	> 5
5	Panicles 7-25 cm long, 0.3-0.8 cm wide; lemma midveins rarely excurrent	Tridens muticus
5	Panicles 5-8(10) cm long, 1.2-2.5 cm wide; lemma midveins always shortly excurrent	Tridenscongestus
1	Primary panicle branches ascending to reflexed or drooping; panicles 1-20 cm wide, open, not spikelike.	> 2
6	All pedicels shorter than 1 mm	Tridens ambiguus
6	Some pedicels longer than 1 mm.	> 7
7	Lateral veins of the lemmas rarely excurrent.	> 8
8	Lemmas 4-6 mm; ligules 0.4-1 mm	Tridens buckleyanus
8	Lemmas 2-3.2 mm; ligules 1.2-3 mm	Tridens eragrostoides
7	Lateral veins of the lemmas commonly excurrent as short points.	> 8
9	Blades 1-5 mm wide; panicles 5-16 cm long	Tridens texanus
9	Blades mostly 3-10 mm wide; panicles 15-40 cm long	Tridens flavus